Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.83   8.797%   $235.9045   $235.90   $235.90   $235.90  
  Purchase #2 $148.80   11.668%   $166.162   $166.16   $166.15   $166.20  
  Purchase #3 $35.97   9.221%   $39.2868   $39.29   $39.30   $39.30  
  Purchase #4 $200.36   11.147%   $222.6941   $222.69   $222.70   $222.70  
  Purchase #5 $30.30   7.682%   $32.6276   $32.63   $32.65   $32.60  
  Purchase #6 $112.65   6.129%   $119.5543   $119.55   $119.55   $119.60  
  Purchase #7 $167.26   13.836%   $190.4021   $190.40   $190.40   $190.40  
  7 purchase totals = $912.17       $1,006.6314   $1,006.62   $1,006.65   $1,006.70